In general, pigments having fine particle diameters are liable to disperse insufficiently in media such as organic solvent and molten resins because the cohesive force between pigment particles tends to be strong. In the case where pigments have insufficient dispersibility and are in an aggregate state, a reduction in tinting strength is caused.
Thus, it is reported that a dispersant to disperse a pigment is used together with the pigment in order to improve the dispersibility of the pigment. In particular, a variety of dispersants for color toners of yellow, magenta, cyan, and black are reported in order to improve the dispersibility of a pigment in toner particles.
For example, PTL 1 discloses, as a technique for dispersing an azo-based pigment in a yellow toner, a technique in which a compound having an azo skeleton structure is used in combination with a binder resin and a pigment to provide a yellow toner having a satisfactory color tone.
PTL 2 discloses, as a technique for dispersing a pigment in a magenta toner, a technique in which a specific polyester-based dispersant is used in combination with a binder resin and a pigment to increase the dispersibility of a magenta pigment and improve the tinting strength of the toner.
PTL 3 discloses, as a technique for improving the dispersibility of a phthalocyanine pigment, an example in which a polymer containing sodium styrenesulfonate serving as a monomer unit is used as a dispersant.
PTL 4 discloses a toner containing a copolymer composed of a styrene-based monomer and an acrylate-based (or methacrylate-based) monomer in order to improve the dispersibility of carbon black in a black toner.